This application claims the priority benefit of Taiwan application serial no. 88113560, filed Aug. 9, 1999.
1. Field of the Invention
The invention relates to a track-number seeking algorithm and a seeking means for an optical storage device, and more particularly, to a track-number seeking algorithm and a seeking means for the dynamic modification of the computation of track numbers in an optical storage device.
2. Description of the Related Art
Tracks in AN optical storage disk are arranged in a spiral fashion. That is, the tracks consist of a continuous spiral track starting from the center of the optical storage disk such that the track appears as a flat coil on the optical storage disk.
A frame and a sector are defined as storage units in the storage structure of the optical storage disk. with consideration for the data storage, the control, the error detection, and the error correction of the optical storage disk. FIG. 1 is a schematic diagram of tracks on an optical storage disk. The tracks consist of frames 104 in the disk 100. Each of the frames 104 is further divided into a subcode region 106a and a data region 106b. The subcode region 106a consists of a Q code and a sector ID 108 for describing properties of the stored data in the frame 104 and the location thereof in the disk 100. A coiled track 102 consists of a plurality of frames cycling around the center of the optical storage disk 100. For example, a coiled track consists of frames 104a, 104b, 104c, and 104d as shown in FIG. 1. Generally, data reading is performed at a constant linear velocity or a constant angular velocity. The spiral circumference of a coiled track close to the center of the optical storage disk is shorter than that close to the edge thereof, i.e. the length of a coiled track close to the center of the optical storage disk is shorter than that close to the edge thereof, and the capacity of a coiled track close to the center of the optical storage disk is smaller than that close to the edge thereof. Thus, when reading at the constant angular velocity, the revolution speed of the motor in a compact disk driver in an interior coil is slower than that in an outer coil.
While randomly accessing the optical storage disk, a pickup head is moved to a desired track along radical direction. This action is called seeking. While reading a particular track in a particular frame, the pickup head is moved along the tangential direction of the coiled track. This action is called track following.
Generally, since the spacing between two adjacent tracks is a constant, for example, the spacing is 1.6 xcexcm in a compact disk (CD), and the spacing is 0.74 xcexcm in a digital versatile disk (DVD), thus, the distance between two arbitrary tracks can be computed through the Q code and the sector ID. According to the relative track number computed from the Q code and the sector ID, the system can give a reference for performing a seeking operation. However, because of a number of reasons such as the relative track number cannot be precisely computed, a seeking operation may cause a deviation, the disk has scratches and defects, the data density during recording depends upon the amount of data, or the data recorded in different disks correspond to different constant linear velocities, the seeking operation may be repeated. Thus, the access time of the compact disk driver is increased, and the performance thereof is affected.
In order to solve the above problems, U.S. Pat. No. 5,195,068 provides a method using a plurality of linear equations to approach a function of absolute time in the Q code (or the sector ID) and absolute track number of the data region. In the seeking operation, the system generates a track crossing number for computing, using the parameters obtained from the linear equations and stored in a memory. However, since the method uses linear equations to approximate a nonlinear function, the track crossing number generated by the system has a greater deviation in some sectors. Thus, the application of the method is restricted.
T.W.P. 081366 provides a more precise method to generate a relative track seeking number and to perform a calibration at different constant linear velocities. According to the method, a nonlinear geometrical relationship between a disk and tracks is used to establish a data table for a reference disk. When the disk is placed in a compact disk driver and the compact disk driver is activated, a calibration process of the disk is performed to generate a constant-linear-velocity index and a time-correction parameter. Using the data table, the constant-linear-velocity index and the time-correction parameter, a relative track seeking number is obtained.
The constant-linear-velocity interior revolution speed of a 1xc3x97speed CD-ROM (compact disk read only memory) is 8 Hz, i.e. 8 revolutions per second (rps). In the case of a 50xc3x97speed CD-ROM, the motor revolution speed is equivalent to 20 times the constant-linear-velocity interior revolution speed of a 1xc3x97speed CD-ROM, i.e. 160 Hz, or 6.25 milliseconds (ms) per revolution. In the average servo system, the seeking process for 200 tracks requires 25 ms. In other words, for the 50xc3x97speed CD-ROM, in the 25 ms, the motor has rotated 4 revolutions.
The constant-linear-velocity interior revolution speed of a 1xc3x97speed DVD-ROM (digital versatile disk read only memory) is 23.1 Hz, i.e. 23.1 rps. In the case of a 20xc3x97speed DVD-ROM, the motor revolution speed is equivalent to 8 times the constant-linear-velocity interior revolution speed of a 1xc3x97speed DVD-ROM, i.e., 160 Hz, or 6.25 ms per revolution. In the average servo system, the seeking process for 200 tracks requires 25 ms. In other words. for the 20xc3x97speed DVD-ROM, in the 25 ms, the motor has rotated 4 revolutions.
According to the above, a deviation of 4 revolutions can be generated when the seeking process starts from the interior tracks to the outer tracks, or from the outer tracks to the interior tracks.
According to the above two methods, the well-known computation of the track seeking number only applies to the case when the pickup head has no relative motion to the disk. However, when the pickup head starts the seeking operation, the disk has a revolution speed, i.e. there is a relative motion. Thus, a deviation of the track crossing number is generated, and the seeking operation is repeated. As a result, the access speed of the compact disk driver becomes slower, and the access time is increased. That is, in the seeking operation, the relative motion between the pickup head and the disk can cause the computing error of the relative track seeking number.
According to the above, the invention provides a track-number seeking algorithm and a seeking means for the dynamic modification of the computation of track numbers in an optical storage device to correct the deviation generated from the motions of the pickup head and the optical storage disk and further to move the pickup head to a target track. Thus, the invention can reduce the average number of track skipping, raise the access speed of the optical storage device and enhance the performance of the optical storage device.
The invention provides a track-number seeking algorithm for the dynamic modification of the computation of track numbers in an optical storage device. The seeking algorithm comprises resetting a rotation number of the disk and a track error zero crossing (TEZC) signal, setting a static relative track seeking number, and performing a seeking operation. The seeking operation comprises reading the rotation number of the disk and a TEZC signal series, computing a residual track number in accordance with the rotation number of the disk and the TEZC signal, and judging whether an overflow flag is sent or not in accordance with a pulse number of a feedback flag. If the overflow flag is sent, the subsequent steps are to increase the rotation number of the disk, to reset the pulse number of the feedback signal, and to judge whether the seeking operation is outward or not. If the overflow flag is not sent, the sequential step is directly to judge whether the seeking operation is outward or not. Then, if the seeking operation is outward and the residual track number is equal to the rotation number of the disk, the seeking operation is concluded; otherwise, the seeking operation is repeated. If the seeking operation is inward and the residual track number is equal to the negative value of the rotation number of the disk, the seeking operation is concluded; otherwise, the seeking operation is repeated.
The invention provides a seeking means for the dynamic modification of the computation of track numbers in an optical storage device to execute the track-number seeking algorithm. The means comprises a down counter, an up counter, a microprocessor etc. The down counter is coupled with the pickup head and the microprocessor while the down counter can receive the static relative track seeking number, enabling signal, and TEZC signal in order to compute the residual track number. The up counter is coupled with a spindle motor and the microprocessor while the up counter can receive the feedback signal of the spindle motor in order to compute the rotation number of the disk and to generate the overflow flag. The microprocessor is coupled with the down counter and the up counter. The microprocessor controls the down counter and the up counter using the enabling signal, sets the up counter by means of a resetting signal, resets the pulse number of the TEZC signal to zero, decides by means of comparing the overflow flag with the residual track number whether the pickup head moves to the target track, and drives the pickup head to the desired position by means of controlling a power driver.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.